Plain English Meaning
A system that fixes small errors in regular GPS signals so the position shown in the cockpit is much more accurate. It does this by checking GPS from ground stations and sending the corrections to the aircraft through extra satellites.
Full Definition
A satellite-based augmentation system that improves the accuracy, integrity, and availability of GPS signals over a wide geographic area. WAAS uses a network of ground reference stations to monitor GPS satellite signals, calculate correction data, and broadcast those corrections through geostationary satellites to suitably equipped aircraft receivers. The corrections allow GPS to be used as a means of for , including with .